The present invention is directed to objects, and particularly, baseball and softball bats, that have a hollow shell composed of filament-wound fiber and resin, and to a method of winding the object and of molding the object.
For many years, softball bats were made of wood. Traditional athletic bats comprised of wood are expensive and consume valuable natural resources. A disadvantage of wood bats is that they frequently break during use. A further disadvantage of wood bats is that they are exceedingly difficult to design for consistent performance, given the inconsistency of the natural material. In addition, wooden bats are made of ash or very hard pine. The sources of such woods are becomingly increasingly rare.
In the past fifteen or twenty years, softball bats made of metal were introduced. Metal bats, although more durable than wood bats, also have problems. One of the many problems associated with a metal bat is that the material is fixed and, as a result, so are the parameters of the material. Metal bats have a fixed density and a given weight. As a result, the engineering parameters that can be varied can only be varied within a limited range.
Currently, metal softball bats are more commonly used than wooden softball bats. A common structure in various non-wooden softball bats includes a hollow bat made with a handle and a hitting surface. The hitting surface includes a tubular portion and a sleeve fit inside the tubular portion. The sleeve is also made of metal. The metal bat and sleeve construction has problems. Several of the problems associated with metal softball bats having metal sleeves stem from the impact or large shock load exerted on the metal bat as a result of hitting a softball. The shock loading produces extremely large forces between the bat and the ball. The result is that the metal bat dents when the ball is hit. Some dents are small and some dents are large. Regardless of the size of the dent, energy is lost on every hit since some of the energy is used to dent the metal rather than to be transferred to the softball. The dents also result in a less durable bat. Once dented, each subsequent hit is a further cold working of the metal. In some instances, a microscopic crack can also be formed as the result of denting of the bat. The crack will get bigger and bigger until the amount of material left fails due to shock loading. Many bats fail quickly. Some bats may fail after as few as twenty-five hits.
More recently, composite bats have been introduced. Composite bats include a reinforced plastic with a metal portion. Examples of U.S. Patents disclosing such composite bats and the problems of such bats are disclosed in the prior, co-pending applications.
Prior, co-pending application Ser. No. 10/438,196 discloses and claims a hollow bat that is comprised of a plurality of composite sleeves made of fibers and resin. The bat is formed and made according to a resin transfer molding process. U.S. Pat. No. 5,811,041, herein incorporated by reference, discloses a resin transfer molding apparatus and method for vacuum transfer molding.
Earlier methods have not completely addressed the problem of producing a hollow bat. In particular, “wet winding” methods, in which the resin is applied to the filament prior to the filament being wound onto the mandrel, require some method, such as a shrink tape, to ensure that the bat is cured under pressure to the designed dimensions. Vacuum transfer mold methods do not work well with bats with thick walls, as it is difficult to fully impregnate the filament. Multiple sleeve methods take considerable time and cost to manufacture the bat.
There is a need for an improved, hollow bat made of filament wound fiber and resin. The inner layers of the bat should be filament wound to save cost and time over using a number of sleeves. The outer layers of the bat should be resin transfer molded. This will ensure thorough filament wet-out throughout the bat and thus ensure uniform properties of performance and durability.
Most composite bats are created by hand using a sock or sheet of woven composite material. While in some instances convenient, the sock or sheet can be expensive and require the manufacture to keep on hand inventory of the material.